There are various legends associated with the Tulsi plant, and therefore, I will just touch upon the most widespread one briefly before moving on to the scientific part:
Vrunda/Vrinda was an ardent devotee of Lord Vishnu, and was married to an Asura Jalandhar. To protect her Suhaag (Husband), she always prayed that no harm ever come to her husband, even though he was a tyrant. But when Jalandhar was finally killed in a battle with Lord Shiva, Lord Vishnu took pity on her. On the request of the other Gods, he took Jalandhar's form and stayed with Vrinda. When she came to know this, Vrinda became enraged and cursed Lord Vishnu to turn into a stone (Saligram). She also fell dead, and a plant (Tulsi) emerged from her. Since then, the "Tulsi Vivah" has been carried on in Hindu homes, where a "Saligram" is married to a "Tulsi" plant. The below photo shows Lord Saligram (black stone), the Tulsi plant and a rare right-faced conch (Shankh).
Tulsi has various medicinal properties, and is probably the most important and frequently used herb in India. Tulsi is :
- Antibiotic and Antifungal
- Effective against Nausea
- Fights Common Cold, Flu and Fever
- Tulsi Juice highly effective against Cough
- Efficient Antioxidant
- Boosts Immunity
As Tulsi is considered the wife of Lord Vishnu, it is taboo in Indian homes to chew the leaves of this plant, though it can be digested as a whole or its juice can be taken.
The actual reason behind not chewing the Tulsi leaves is due to its mercuric content. German researchers have discovered that the leaves of the holy Tulsi plant contains traces of mercury. If the leaves are chewed, the mercury may damage the teeth. But when taken as a whole, the mercury is found beneficial for the digestive system.
This mercury content is now being used in anti-cancer drugs.
Thus, by weaving a legend around the Tulsi plant, the ancient Vedic Indians accomplished 2 things: firstly, the Tulsi plant would be worshipped in all homes, and thus its medicinal properties would be effectively utilised. Secondly, by calling it Lord vishnu's wife, it could not be chewed, thus preventing damage to our teeth.